The animal called cacus is found in some medieval encyclopedias. It appears to be a misreading of the myth of Cacus, a monstrous (human) shepard who ate human flesh. The myth says that he stole cattle from Hercules, dragging them backward by their tails into his cave, for which Hercules killed him. He is said to have shot fire from his chest when angry, and was bristly all over like a boar.

The cacus signifies angry people who, unable to restrain themselves from their increasing anger, pour out insults that inflame others to anger and hatred. Such people are dangerous because they draw others toward the gates of hell, even the rational and religious, for it is difficult to control one's anger at all times.

The usual illustration shows Cacus as an indeterminate beast (lion, wolf, bear) in a cave, pulling cattle by their tails.